Many freezing and cooking operations utilize conveyor belts that carry workpieces through a processing section of a freezer or an oven or even a series of freezers or ovens. In order to achieve the desired amount of freezing or cooking, the conveyor belt speed is set to a speed that will fully freeze or cook the largest of the workpieces. This is to ensure that all pieces meet the necessary minimum requirements, many times mandated by regulations. While this accomplishes the desired goal of not allowing workpieces to pass unprocessed or under pressure through the freezer or oven, the operation may be inefficient, since many of the workpieces will be unnecessarily overprocessed. Ideally, each workpiece would spend only the amount of time in the freezer or oven that is required to fully freeze or cook it to the required specifications, without significant loss of freezer or oven capacity.
One approach to this problem has been to “piece sort,” meaning employing multiple conveyor belts within a single oven or freezer with each belt running at a different speed. This arrangement allows the workpieces to be sorted by size ahead of the processing operation. In a three-conveyor system, for example, the smallest pieces are placed on the fastest moving belt, the medium-sized pieces are placed on the next slowest belt, and the largest pieces are placed on the slowest belt. The size range for each conveyor may be determined from a manual sampling of workpiece sizes. By knowing the performance characteristics of the processing operation for the particular workpiece, each belt speed can be adjusted for a population of workpieces that fall within a certain size range. Utilizing multiple conveyor belts, and sorting ahead of the processing operation, may provide a temporary solution, but this situation may be short-lived. Due to the ever-changing variation in the sizes of workpieces, the initial sorting criteria may not be representative as time progresses. The inevitable result is a shift of product from the fastest belt to the slower belts if the average size of the workpieces was to increase. Conversely, if the average size was to decrease, the products would start to accumulate on the fastest moving belt. Too much product on one belt when the other belts are not at full capacity is also not utilizing resources to their fullest capability.
Another method of sorting is called “even flow,” meaning the lines are kept as full as possible regardless of the workpiece weight or size. This practice leads to the possibility that workpieces will be over- or underprocessed.
An “even flow” sort alone may require overcooking or overfreezing product as the size distribution changes, without a change in retention time/conveyor speed. “Piece sorting” alone can move all product to a single retention time, making a single retention time a bottleneck, while other retention time line or belts are underutilized. Thus, the conventional ways of sorting can eventually lead to gross inefficiencies.
What is lacking in the art is a method of sorting by size combined with the ability to provide even product flow to maintain the belt's loading at its optimum. The present invention addresses this need and seeks to provide further related advantages.